Interference from external magnetic fields is a serious problem in semiconductor devices that include magnetic materials. Such devices can include magnetic field sensors, magnetoresistive random access memory (hereinafter referred to as “MRAM”) devices, or the like, and typically utilize the orientation of a magnetization vector for device operation. In MRAM devices, for example, the stability of the nonvolatile memory state, the repeatability of the read/write cycles, and the memory element-to-element switching field uniformity are three of the most important aspects of its design characteristics. These characteristics depend on the behavior and properties of the magnetization vector.
Storing data in a MRAM device is accomplished by applying magnetic fields and causing a magnetic material in the MRAM device to be magnetized into either of two possible memory states. Recalling data is accomplished by sensing the resistive differences in the MRAM device between the two states. The magnetic fields for writing are created by passing currents through conductive lines external to the magnetic structure or through the magnetic structures themselves.
If a magnetic field is applied to a MRAM device during writing, then the total field incident to the MRAM device may be less than that required for writing which can cause programming errors. In addition, a typical MRAM architecture has multiple bits that are exposed to magnetic fields when one MRAM device is programmed. These one-half selected MRAM devices are particularly sensitive to unintended programming from an external magnetic field. Further, if the magnetic field is large enough, MRAM devices may be unintentionally switched by the external magnetic field even in the absence of a programming current.
A method to decrease the effects of magnetic field interference is to magnetically shield the electronic circuit components. Prior art magnetic shielding solutions typically involve using a lid or enclosure surrounding a device, wherein the lid or enclosure may be connected to a ground potential. However, prior art shielding solutions are often too expensive and not easily integrated with the magnetic devices.
Accordingly, it is an object of the present invention to provide a new and improved magnetic shielding solution for electronic circuits which include magnetic materials.